This invention generally relates to an improved lock rod clamping apparatus for detachably connecting a tool unit to a tool supporter, and is particularly concerned with such an apparatus having a self-locking lock rod that can be pulled into a locking position by -means of a low pressure, pneumatic actuator. The lock rod may further include recesses adjacent to its ramp portions for receiving one or more locking spheres.
Clamping mechanisms for detachably connecting a tool unit to a tool supporter are well known in the prior art. Such mechanisms are typically used in machining operations where the tool unit holds a cutting insert that is moved into and out of cutting engagement with a rotating workpiece. The clamping apparatus allows different tool units holding different cutting inserts to be quickly attached to and detached from the tool supporter which in turn is connected to a lathe or other device, that controls the movement of the tool unit with respect to the workpiece.
One of the commercial clamping mechanisms includes a cylindrically-shaped canister member that is matable with the tubular end of a tool unit and which includes apertures for admitting locking elements into locking engagement with recesses present in the tool unit. The locking elements, which are typically spherical, are radially moved through the apertures in the canister member by means of a reciprocating lock rod having cams that engage the locking elements. Examples of such clamping mechanisms are disclosed in U.S. Pat. Nos. 4,708,040; 4,747,735; 4,836,068, and 4,932,295, each of which is assigned or co-assigned to Kennametal Inc., located in Latrobe, Pa.
A side, cross-sectional view of such a prior art clamping mechanism 35 is illustrated in FIGS. 3 and 4. Such a mechanism 35 includes a cylindrically-shaped canister member 39 mounted within a housing 41 formed from a coupling member 43. The canister member 39 includes a pair of opposing apertures 54a,b in the form of cylindrical bores through the tubular wall of the member 39. The walls 56 of the apertures 54a,b, are orthogonal with respect to the axis A of reciprocation of the lock rod 60. The inner diameter of the cylindrical bores forming the apertures 54a,b closely approximates the outer diameter of spherical locking elements 57a,b. The reciprocating lock rod 60 includes a distal end 62 that is slidably mounted within the cylindrical interior of the canister member 39. The distal end 62 of the lock rod 60 includes cams 64a,b which include spherical depressions 66 that taper off into ramp portions 68. The proximal end 69 of the lock rod 60 is connected to an actuator 73 formed from a stack of Bellville washers 74 that are slidably and concentrically disposed around the proximal end 72.5 of the canister member 39. These springs 74 are captured between support plate 45 and a spring retainer 73.5 connected to the proximal end 69 of the lock rod, and provide a pulling force that draws the lock rod 60 into the position shown in phantom. In this position, the ramp portions 68 of the cams 64a,b radially push the locking spheres 57a,b through the cylindrical apertures 54a,b in the canister member 39 and into engagement with angled wall portions 30 present in the frustro-conically shaped tool unit 10. This engagement lockingly secures the tool unit 10 to the tool supporter 37.
While such a prior art locking mechanism has proven its capability of quickly, conveniently, and rigidly attaching a tool unit to a tool supporter, the applicant has observed several areas where the performance of such a mechanism may be improved. Specifically, the applicant has observed that if the clamping mechanism could be modified to render the lock rod self-locking, then the need for any kind of device for continuously applying a large pull-back force on the rod to maintain it in a locked position could be eliminated. Presently, this pull-back force is provided by spring-type actuators such as Bellville washers, or hydraulic cylinder-type actuators. Such actuators serve not only to draw the lock rod into the position illustrated in FIG. 4, but to maintain the lock rod in such a position until it is desired to disengage the clamping mechanism from the tool unit.
The applicant has also observed that if the amount of pull-back force necessary to pull the lock rod into a locking position (which may be about 2000 pounds) could be lowered, then the spring-type or hydraulic actuators used in the prior art could be replaced with a smaller and lighter pneumatic cylinder. Such a pneumatic cylinder could advantageously be powered by the 80 psi compressed air available in virtually all machine shops.
It would further be advantageous if the resulting gripping force could be increased, thereby also increasing tool rigidity and cutting accuracy.
Finally, it would be advantageous if all of these objects could be achieved with only a minimal amount of modification to the shapes of existing parts so that a conventional clamping mechanism of the type previously described could easily be converted into such a clamping mechanism.